Air depolarized battery including regenerative lime sheet



Feb. 24, 1970 C A. GRULKE AIR DEPOLARIZED BATTERY INCLUDING REGENERATIVELIME SHEET Filed Aug. 10, 1967 3 Sheets-Sheet l PULP WA TER DISPERSIONMIXER L IME CALCIUM H VDROY/DE STORAGE METHA/VOL COLLOID MILL swamronmmcnros mom mxsn any INVENTOR A RL AGRULKE CAST MIXER Feb. 24, 1970c. A. GRULKE E I 3,497,391

AIR DEPOLARIZED BATTE Y INCLUDING REGENERATIVE LIME SHEET Filed Aug. 10,1967 3 Sheets-Sheet :5

600 MILLIAMPS CONTINUOUS DRAIN AT ROOM TEMPERATURE IIG LIME PELLETSV I00um can f 1 LIME swears GRAMS OF ZINC/LITER J I I l I I e00 600 I000 1200I400 AMPERE HOURS FIG.4. Y

INVENTOR United States Patent 3,497,391 AIR DEPOLARIZED BATTERYINCLUDING REGENERATIVE LIME SHEET Carl A. Grulke, Berea, Ohio, assignorto Union Carbide Corporation, a corporation of New York Filed Aug. 10,1967, Ser. No. 659,810 Int. Cl. H01m 29/04 US. Cl. 13686 3 ClaimsABSTRACT OF THE DISCLOSURE An alkaline primary galvanic battery of thetype employing a zinc anode including a thin porous regenerative limesheet comprising colloidal lime particles and dispersed cellulose fibersbonded together with an organic binder insoluble in the alkalineelectrolyte of the battery.

The present invention relates to the regeneration of alkalineelectrolytes in primary galvanic batteries of the type employing a zincanode. More specifically, the invention concerns a novel and improvedregenerative lime material for use in precipitating dissolved zinc fromthe alkaline electrolyte of a conventional type of air-depolarizedprimary battery, and to a process for preparing the regenerative limematerial.

In the conventional type of air-depolarized primary battery employing azinc anode, the electrolyte is an alkaline solution such as potassium or-sodium hydroxide. During discharge of the battery, the electrolyte isgradually exhausted by chemical combination with the zinc anode. Asdischarge proceeds, there is a build-up of dissolved zinc within theelectrolyte which may reach a high level. Because of this build-up ofdissolved zinc and the consequent electrolyte depletion, the voltagelevel and efficiency of the battery may be seriously affected.

It has long been recognized that lime, i.e., slaked lime (calciumhydroxide). is an effective regenerative agent for the precipitation ofdissolved zinc from the alkaline electrolyte of a wet-type alkalineprimary galvanic battery employing either an air-depolarized or copperoxide cathode and a zinc anode. This basic concept of employing aregenerative lime material within the electrolyte was first disclosed inUS. Patents. Nos. 1,835,867 and 1,864,652 to Heise and is still widelyused today in the battery industry. Subsequent work in this field haslead to the development of several different forms of the regenerativelime material. For example, in US. Patent No. 2,180,955 to Heise andSchumacher, there is disclosed a lime material in the form of a briquetor lime cake for use as the regenerative agent in an air-depolarizedprimary battery. The lime briquet or so-called X-cake was made bymolding the lime particles together with a bonding agent and swellablefibers. The swellable fibers served as socalled extending agents for thebriquet. The briquet offered the advantage in that considerably more ofthe lime material could be incorporated within a given volume of thebattery.

Another type of lime material that has been widely used is disclosed inUS. Patent No. 2,450,472. This material consisted of lime particlesbonded together to form small rigid, permeable granules about A; inch indiameter. The binder used for the lime particles may be any one of anumber of electrolyte insoluble and chemically non-reactive materials.Examples of suitable binder materials include sodium silicate or sodiumzincate for permanent cementing eflect and atmospheric carbon dioxidewhich reacts with moist lime to produce some calcium carbonate as abonding agent. Organic binders such as polystyrene, polyethylene,polyvinyl resins and the like have also been used as the bindermaterial. The preferred ice binder material is calcium chloride whichwas used in proportions of approximately grams of calcium chloride toone liter of water. The mixture was added to the lime particles as themoistening agent and produced an oxychloride cement by chemicalcombination with the lime which served as the bonding agent.

While these prior art forms of regenerative lime material have generallyproven effective for precipitating dissolved zinc from the alkalineelectrolyte of primary galvanic batteries, it has been foundnevertheless that these forms of regenerative lime material are subjectto certain limitations and consequently they have not proven entirelysatisfactory. One serious limitation resides in the fact that due totheir relatively large size or dimension and in particular the thicknessof the lime briquet and diameter of the lime granules, a substantialportion of the regenerative lime is rendered inaccessible for reactionwith the zinc in the electrolyte. This is so since the reaction productbetween the zinc and the lime forms on the surface of the regenerativelime body and tends to block access to the innermost portion of thelime. Thus, it has not been heretofore possible to achieve maximumeffective use of the available lime in the batteries.

It is an object of this invention to provide a novel and improvedregenerative lime material for use in a primary galvanic battery of thetype employing an alkaline electrolyte and a zinc anode.

More specifically, another object of this invention is to provide anovel and improved regenerative lime material which is capable of moreefiiciently precipitating dissolved zinc from the alkaline electrolyteof an air-depolarized primary battery.

Still another object of this invention is to provide a novel andimproved process for preparing the regenerative lime material.

The foregoing and other objects of this invention are achieved by anovel and improved regenerative lime material provided in the form of athin porous sheet. The lime sheet is composed of colloidal limeparticles and dispersed cellulose fibers bonded together with a smallamount of an organic binder which is insoluble but swellable to acontrolled degree, in an alkaline electrolyte. The cellulose fibersserve as both a porosity-promoting diluent and support for the colloidallime particles. Additionally, the fibers together with the swellablebinder provide electrolyte access to the lime particle surfaces in allportions of the sheet.

In the accomapnying drawings:

FIGURE 1 is a flow diagram illustrating the steps in the preparation ofthe lime sheet of the invention;

FIGURE 2 is a perspective, partially cut-away view of a typicalair-depolarized primary battery incorporating the lime sheets of theinvention; and

FIGURES 3 and 4 are graphs illustrating the comparative effectiveness ofthe lime sheets and known regenerative lime materials of the prior art.

The process for preparing lime sheets in accordance with the inventionis illustrated in the flow diagram of FIGURE 1. The lime sheets areprepared by blending a colloidal suspension of micromilled lime withdispersed cellulose pulp, preferably a sulfate process pulp, togetherwith a small amount of an organic binder. A preferred organic binder ishydroxyethylcellulose insolubilized in alkaline solution by a suitablealdehyde or methylol treatment. The organic binder is added to the blendin order to improve the adhesion between the colloidal lime particlesand the cellulose fibers and to thus effectively increase the strengthof the finished lime sheets. The thus formed slurry is then formed orcast into thin porous sheets which are subsequently dried and cut to thefinished dimensions desired. Optionally, the formed sheets may be castdirectly to the necessary dimensions for incorporation into the battery.

In the practice of the invention, it is important that the lime be firstmicromilled to an extremely fine particle size in order to effectivelyincrease or maximize the available lime surface for reaction with thedissolved zinc in the electrolyte. Preferably, the particle size of thelime after milling is in the range of about 0.01 to about 0.1 micron. Itis also essential that the lime sheets be formed or cast to a relativelythin dimension of the order of approximately to inch in thickness. Thethinness of the lime sheets is an important factor in promoting maximumeffective use of the available lime.

Depending on the particular application, the composition of the finisheddried lime sheet may vary in the ratio of approximately 75 to 95 percentlime and to 25 percent cellulose fibers based on the weight of thefinished sheet. The preferred range of the lime is between about 80 to90 percent by weight of the sheet. Formulations containing as little aspercent lime may be useful under special conditions.

While the lower percentage of cellulose fiber to be used is not toocritical so long as the physical integrity of the sheet can bemaintained both during preparation of the sheet and during normaloperation of the battery, high concentrations of the cellulose fiberabove about percent should generally be avoided since the larger amountsof cellulose may cause undesirable swelling when the sheets are placedin contact with the electrolyte of the battery. Additionally, the use oflarger amounts of the fiber prevents incorporation of suflicient lime tooperate the battery effectively under normal conditions. The finishedlime sheet may contain a small amount of residual moisture generally notin excess of about one to two percent by weight.

The binder used in preparing the lime sheet must be stable in causticsolution, either potassium or sodium hydroxide. The binder may bedefined as an initially water-dispersible resin insolubilized, as in thecase of hydroxyethylcellulose, preferably through an aldehyde ormethylol treatment to a controlled swellability. The ether linkage soformed is resistant to prolonged exposure to caustic. The preferredbinder for preparing the lime sheet is insolubilizedhydroxyethylcellulose. Other suitable binder materials which may beinsolubilized in a similar manner include precooked starch, polyacrylicacid, polyvinyl alcohol, polyvinyl formal, and polyacrylamide resin, forexample. The preferred binder, i.e., insolubilizedhydroxyethylcellulose, is employed in an amount of about 0.5 to about2.5 percent based on the weight of lime employed.

The degree of binder swelling when in contact with the causticelectrolyte can be effectively controlled by the use of heat and by theaddition of a cross-linking agent in the form of aldehydes. Suitablealdehydes include formaldehyde, glyoxal and a.-hydroxyadipaldehyde. Thepreferred cross-linking agent for hydroxyethylcellulose is formaldehydewhich is employed in amounts of between about 2 to 5 percent of a 36percent aqueous solution based on the weight of thehydroxyethylcellulose binder. Higher concentrations of the cross-linkingagent may be preferred. A concentration as high as 1:1 ratio with thebinder may be used if desired. Variations in the insolubilizingtreatment may be made to correspond with the particular chemicalstructure of the selected binder.

Referring now to FIGURE 2 of the drawing, there is shown a typicalair-depolarized battery embodying the invention. As shown, the batteryhas an outer rectangular casing 10 having an open end which is closed bya cover 12. The battery casing 10 and cover '12 are suitably made of acaustic resistant material such as an epoxy or vinyl resin, for example.Within the battery casing 10 is an air-depolarized carbon cathode 14which is suitably activated by conventional methods known in the art.The carbon cathode 14 is mounted to the cover 12 and has a portion ofits top surfaces protruding therethrough as at 16 in order to provideaccess of air to the activated surfaces of the cathode 14. Disposed oneach side of the carbon cathode 14 is one of a pair of zinc anode bars,one of which is shown at 18. The anode bars 18 are suitably mounted ateach end within a pair of anode supports 20, 22 provided on oppositesides of the battery casing 10. The anode supports 20, 22 are suitablymade of a caustic resistant material. If desired, the anode supports 20,22 may be integrally formed within the side walls of the battery casing10. The battery casing 10 is filled with an alkaline electrolyte,suitably a 6.25 normal solution of potassium hydroxide.

In accordance with the invention, the air-depolarized primary battery isprovided with a plurality of lime sheets as indicated at 24. The limesheets 24 are stacked together and mounted within the battery with theflat surfaces thereof lying in a direction substantially perpendicularto the bottom of the battery casing 10. Preferably, as shown, the stackof lime sheets 24 are oriented diagonally within the battery casing 10in order to provide for uniform circulation of the electrolyte aroundthe edge-s and bottom of the sheets.

The following example illustrates in greater detail the process forpreparing the lime sheets of the invention. The first step in thepreparation of the lime sheets is micromilling of the lime to reduce itsparticle size and thereby increase its available surface area. Chemicalgrade lime is preferred. A 30 percent lime-in-water mixture is preparedand micromilled through a colloid mill. The initial viscosity of themixture is about 500 centipoise. Milling action is terminated when themixture reaches a viscosity of between about 18,000 to 20,000centipoise. During the milling operation, the temperature of the mixturewill increase to between about F. to F.

Cellulose pulp is next prepared by mixing dry cellulose fibers andwater. The preferred pulp is a sulfate bleached pulp. In forming thepulp, the dry fibers should be beaten in the water mixture sufficientlyto preclude the presence of course fibers. Excess water is then drainedfrom the pulp. The pulp should not be too dry, however, so as to avoidagglomeration of the fibers during preparation of the pulp.

The binder is prepared by mixing the hydroxyethylcellulose with about 2to 5 percent of a 36 percent solution of formaldehyde which is used as across-linking agent. Generally, about 18 milliliters of a 36 percentsolution of formaldehyde in water may be used for a fifty pound batch oflime. The hydroxyethylcellulose is added in an amount of about 0.5percent based on the weight of lime employed. The mixture is dilutedwith a fifty-fifty (by volume) methanol-water solution (approximately1.5 liters are added per 225 grams of the binder). The crosslinkingagent should be thoroughly intermixed with the binder.

The colloidal lime suspension and cellulose pulp are then mixed togetherand agitated for time sufficient to obtain an intimate mixture of thelime and fibers. The hydroxyethylcellulose binder as preparedabove isthen added and sufiicient stirring is employed to obtain a smoothconsistency within the mixture. The resultant blend is spread in a thinlayer on a glass plate and then calendered in sheets which aresubsequently dried, preferably in a CO -free atmosphere, on an oven atabout 130 C. (preferably no higher than 138 C.) to remove all but asmall amount of water and to set the binder. The flat surfaces of thesheets are preferably corrugated or otherwise roughened in order toexpose more surface to the electrolyte. The sheets are then cut to fitthe particular dimension of the battery. If the sheets are not to beused Within a short period, they should preferably be stored in a C0free atmosphere in order to avoid carbonate formation. Reaction of theportion of the lime in the sheets with CO in the atmosphere will reducethe total lime available for reaction with the dissolved zinc and thusdetract from the high efficiency exhibited by this form of regenerativelime material.

It will of course be obvious to one skilled in the art that variationsin raw materials may occur which may necessitate certain changes indetailed process conditions in order to produce thin lime sheets havingthe desired characteristics of porosity, strength to withstand handlingand storage, and resistance to degradation in the battery electrolyte.

To compare the performance of the lime sheets of the invention, a numberof air-depolarized primary batteries of a construction similar to thatillustrated in FIGURE 2 were assembled employing either lime briquets,lime pellets or the lime sheets prepared in accordance with theinvention. The batteries were assembled employing one activated carboncathode, two zinc anodes and a 6.25 molar KOH electrolyte. The batterycasing was made of a caustic resistant material, i.e., a vinyl resin,which was transparent so that the formation of precipitate and theblanketing of the lime by the precipitate could be observed. The limebriquets used in some of the batteries were provided in the form ofrelatively thick cakes of about A inch to /2 inch in thickness and weremade by molding lime with wood floc or cellulose floc and cotton thread.The lime sheets were stacked vertically within the. bottom of thebattery casing and preferably in a position perpendicular to the planeof the electrode faces. About fifty lime sheets approximately 4 /2 by 5by A inch and containing approximately 80 to 85 percent lime wereemployed. Each of the batteries assembled had exactly the same weight ofzinc, lime and electrolyte. The total volume was substantially the samefor all the batteries.

The air-depolarized primary batteries so assembled V were then tested bysubjecting each battery to one of two drain conditions, i.e. 600milliamperes and 150 milliamperes, at substantially room temperaturesimulating the approximate conditions under which the batteries wouldnormally be operated. During the test, electrolyte solutions weresampled at every 100 ampere hours and the particular dissolved zincconcentration for each battery was then determined.

FIGURES 3 and 4 graphically depict the relative performances of thebatteries tested. It will be readily seen from these curves that theconcentration of zinc in the electrolyte is considerably less for thebatteries employing the lime sheets of the invention. Thus it may befairly concluded that under the particular test conditions, i.e.,continuous drain at room temperatures, the lime sheets are far moreefficient in precipitating dissolved zinc from the electrolyte solutionof the batteries.

To further illustrate the effectiveness of the invention another seriesof tests were conducted using identical airdepolarized batteries inwhich the total ampere hour capacity was recorded at the end of theuseful life of the batteries. These discharge tests were conducted at acontinuous drain of 600 milliamperes at room temperature and at 27 F.The results of the test are given in Tables I and II below:

TABLE I.AMPERE-HOUR CAPACITY AT 27 F.

Lime form: Ampere-hours 1 Cakes 1319 Pellets 1214 Sheets 1703 1 Averagecapacity of three batteries.

TABLE II.AMPERE-HOUR CAPACITY AT ROOM TEMPERATURE Lime form:Ampere-hours 1 Cakes 1266 Pellets 1603 Sheets 1573 1 Average capacity ofthree batteries.

From the above tables it will be seen that the airdepolarized batteriesusing the lime sheets of the invention averaged at least 25% moreservice, as expressed in terms of ampere hour capacity, than thebatteries employing the lime cakes as the regenerative lime material. Ata temperature of 27 F., the lime sheets produced substantially betterperformance than either the lime pellets or lime cakes of the prior art.

What is claimed is:

1. An air-depolarized primary galvanic battery comprising, incombination, a casing having a cover therefor, and in said casing, azinc anode, an activated carbon cathode and an alkaline electrolyte, andin contact with said alkaline electrolyte, at least one regenerativethin lime sheet comprising from about to percent by weight colloidallime particles and from about 5 to 25 percent by weight dispersedcellulose fibers bonded together with an organic binder insoluble insaid alkaline electrolyte, said organic binder being present in anamount of about 0.5 to about 2.5 percent based on the weight of lime inthe sheet.

2. The air-depolarized primary galvanic battery of claim 1 wherein aplurality of the regenerative lime sheets are stacked together anddisposed at the bottom of said casing with the flat surfaces thereoflying in a plane substantially perpendicular to an active surface ofsaid anode.

3. The air-depolarized primary galvanic battery of claim 2 wherein thecasing is of rectangular shape and wherein the stack of regenerativelime sheets is disposed diagonally within the bottom of the casing.

References Cited UNITED STATES PATENTS 1,835,867 12/1931 Heise 136-154 X1,864,652 6/1932 Heise 136154 2,180,839 11/1939 Schumacher et al. 136l362,180,955 11/1939 Heise et al 136136 X 2,450,472 10/1948 Dunham et al136-164 ALLEN B. CURTIS, Primary Examiner U.S. Cl. X.R. 136136, 164

